1. Field of the Invention
The present invention relates to a piezoelectric ceramic composition of a composition not containing lead and a method of production of the same and to a piezoelectric element and dielectric element using the piezoelectric ceramic composition as materials.
2. Description of the Related Art
In the past, as a piezoelectric ceramic composition, a PZT (PbTiO3—PbZrO3) component-based ceramic containing lead has been used. This is because the above PZT exhibits large piezoelectric properties and has a high mechanical quality factor superior in long-term stability and enables the easy fabrication of materials of various properties required for applications such as sensors, actuators, and filters.
Further, PZT has a high relative dielectric constant, so can also be used as a capacitor etc.
While a piezoelectric ceramic composition comprised of PZT has superior properties, it includes lead among its component elements, so harmful lead leaches out from the industrial waste of products containing the PZT and therefore environmental pollution is liable to be caused. The rising awareness of such environmental issues in recent years has made difficult the production of products which might become causes of environmental pollution such as with PZT. Therefore, development of a piezoelectric ceramic composition of a composition not containing lead is being sought. A piezoelectric ceramic composition of the general formula (K1-xNax)NbO3 (where, 0<x<1) has become the focus of attention. (See Journal of the American Ceramic Society, U.S., 1962, vol. 45, no. 5, p. 209.)
(A) Problem to be Solved I
A piezoelectric ceramic composition of the general formula (K1-xNax)NbO3 (where, 0<x<1) is difficult to fire, so hot press sintering is necessary. Therefore, there was the problem that the production costs became high.
Further, there was the problem that the piezoelectric ceramic composition of the above general formula suffered from low properties such as the piezoelectric d31 constant, electromechanical coupling coefficient Kp, and Curie temperature Tc. Therefore, application was difficult to piezoelectric elements requiring high piezoelectric d31 constants and electromechanical coupling coefficients Kp such as piezoelectric actuators, piezoelectric filters, piezoelectric vibrators, piezoelectric transformers, piezoelectric ultrasonic motors, piezoelectric gyrosensors, knock sensors, yaw rate sensors, air bag sensors, back sonar, corner sonar, piezoelectric buzzers, piezoelectric speakers, and piezoelectric ignitors. Further, since the Curie temperature Tc is low, there was the problem that the piezoelectric properties deteriorated under a high temperature environment.
The invention was made in view of the above problem and has as its object to provide a piezoelectric ceramic composition not containing lead, able to be sintered at ordinary pressure, and superior to the past in at least one of the properties unique to piezoelectric ceramic compositions such as the piezoelectric d31 constant and a method of production of the same and a piezoelectric element and dielectric element utilizing that piezoelectric ceramic composition.
(B) Problem to be Solved II
A piezoelectric ceramic composition of the above general formula (K1-xNax)NbO3 (where, 0<x<1) suffers from the problem of low piezoelectric properties such as the piezoelectric d31 constant, electromechanical coupling coefficient Kp, piezoelectric g31 constant, and mechanical quality factor Qm. Therefore, application was difficult to a piezoelectric elements requiring a high piezoelectric d31 constant such as piezoelectric actuators, piezoelectric filters, piezoelectric vibrators, piezoelectric transformers, piezoelectric ultrasonic motors, piezoelectric gyrosensors, knock sensors, yaw rate sensors, air bag sensors, back sonar, corner sonar, piezoelectric buzzers, piezoelectric speakers, and piezoelectric ignitors.
Further, since the piezoelectric ceramic composition of the above general formula has low dielectric properties such as the relative dielectric constant ∈33τ/∈0 and dielectric loss tan δ, there was the problem that application was difficult to a dielectric element such as a capacitor.
The present invention was made in view of the above problem in the prior art and has as its object to provide a piezoelectric ceramic composition not containing lead, having high piezoelectric properties and dielectric properties, and superior in at least one of the piezoelectric d31 constant, relative dielectric constant, dielectric loss, and Curie temperature Tc and a method of production of the same and a piezoelectric element and dielectric element utilizing that piezoelectric ceramic composition.
(C) Problem to be Solved III
A piezoelectric ceramic composition of the above general formula (K1-xNax)NbO3 (where, 0<x<1) suffers from the problem of low piezoelectric properties such as the piezoelectric d31 constant, electromechanical coupling coefficient Kp, piezoelectric g31 constant, and mechanical quality factor Qm and low dielectric properties such as the relative dielectric constant ∈33τ/∈0 and dielectric loss tan δ. Therefore, application was difficult to piezoelectric elements requiring a high piezoelectric d31 constant and electromechanical coupling coefficient Kp such as piezoelectric actuators, piezoelectric filters, piezoelectric vibrators, piezoelectric transformers, piezoelectric ultrasonic motors, piezoelectric gyrosensors, knock sensors, yaw rate sensors, air bag sensors, back sonar, corner sonar, piezoelectric buzzers, piezoelectric speakers, and piezoelectric ignitors and to dielectric elements such as capacitors.
To solve this problem, in addition to the piezoelectric ceramic composition of the above general formula (K1-xNax)NbO3, various piezoelectric ceramic compositions of compositions not containing lead are being developed, but almost all of these cannot withstand practical use. Further, in general the piezoelectric d31 constant and mechanical quality factor Qm are contradictory in relationship, so it is particularly difficult to obtain a piezoelectric ceramic composition superior in both of the piezoelectric d31 constant and mechanical quality factor Qm.
The present invention was made in view of the above problem in the prior art and has as its object to provide a piezoelectric ceramic composition not containing lead, having high piezoelectric properties and dielectric properties, and superior in both of the piezoelectric d31 constant and mechanical quality factor Qm and a method of production of the same and a piezoelectric element and dielectric element utilizing that piezoelectric ceramic composition.
(D) Problem to be Solved IV
A piezoelectric ceramic composition of the above general formula (K1-xNax)NbO3 (where, 0<x<1) suffers from the problem of being difficult to sinter. Therefore, the sintered piezoelectric ceramic composition features a low apparent density and tends to have a large number of pores in its surface and inside. Therefore, a conventional piezoelectric ceramic composition of the above general formula (K1-xNax)NbO3 suffered from the problem of a susceptibility to a drop in its mechanical strength.
The present invention was made in view of the above problem in the prior art and has as its object to provide a piezoelectric ceramic composition not containing lead, having a high apparent density, and having a low porosity and open porosity and a method of production of the same and a piezoelectric element and dielectric element utilizing that piezoelectric ceramic composition.
(E) Problem to be Solved v
A piezoelectric ceramic composition of the above general formula (K1-xNax)NbO3 (where, 0<x<1) suffers from the problem of low piezoelectric properties such as the piezoelectric d31 constant, electromechanical coupling coefficient Kp, piezoelectric g31 constant, and mechanical quality factor Qm. Therefore, application is difficult to piezoelectric elements requiring a high piezoelectric d31 constant and electromechanical coupling coefficient Kp such as piezoelectric actuators, piezoelectric filters, piezoelectric vibrators, piezoelectric transformers, piezoelectric ultrasonic motors, piezoelectric gyrosensors, knock sensors, yaw rate sensors, air bag sensors, back sonar, corner sonar, piezoelectric buzzers, piezoelectric speakers, and piezoelectric ignitors.
Further, since the piezoelectric ceramic composition of the above general formula has low dielectric properties such as the relative dielectric constant ∈33τ/∈0 and dielectric loss tan δ, there was the problem that application was difficult to a dielectric element such as a capacitor.
The present invention was made in view of the above problem in the prior art and has as its object to provide a piezoelectric ceramic composition not containing lead, having high piezoelectric properties and dielectric properties, and superior in at least one of the piezoelectric d31 constant, mechanical quality factor Qm, and relative dielectric constant and a method of production of the same and a piezoelectric element and dielectric element utilizing that piezoelectric ceramic composition.